Conventionally, a developing unit includes a developer-carrying member such as developing sleeve, for example. The surface of the developer-carrying can be treated with sandblasting to make a roughness condition on the surface of the developer-carrying member.
The developer-carrying member having a sandblasted surface can suppress a slipping of the developer on the developer-carrying member (e.g., developing sleeve) rotating at a high speed and a resultant accumulation of the developer on the developing sleeve. With such surface treatment on the developer-carrying member, degradation of image quality on a recording sheet may be prevented.
Sandblasting can be conducted by blasting particles on a surface of the developer-carrying member (e.g., a developing sleeve) made of metal (e.g., aluminum) to form convex and concave portions on the surface of the developer-carrying member, wherein such convex and concave portions have sharp profiles and a convex portion and an adjacent concave portion may exist with a relatively smaller interval therebetween.
Such sandblasted developer-carrying member can suppress slipping of developer on the developer-carrying member rotating in a high speed because the developer can be carried by the convex portions having sharp profiles.
However, such sandblasted surface of the developer-carrying member may have some drawbacks as to durability. Fox example, the sandblasted surface of the developer-carrying member become abraded over the time, the convex portions may lose their sharpness and the edges of the convex portions may become rounded. Such rounded convex portions may be less likely to carry the developer. In such a case, degradation of developer transportability on the developer-carrying member may happen.
Furthermore, the convex portions having sharp profiles may scrape toners and external additives on the carrier, and such scraped toners and external additives may drop into tiny concave portions on the developer-carrying member.
Such toners and external additives in the tiny concave portions may be fixed on the developing sleeve by heating, whereby such phenomenon may change the electrical resistance of the developer-carrying member. In such a case, degradation of developer transportability on the developer-carrying member may occur.
One known background image forming apparatus includes a developer-carrying member (e.g., developing sleeve) having been treated with a roughness treatment. Such developer carrying member has a surface which has a ten-point average roughness of from 4 μm to 20 μm, and an average interval Sm of from 30 μm to 80 μm, for example, wherein the average interval Sm indicating a surface condition is explained as below with respect to FIG. 1.
As shown in FIG. 1, a measurement-range length “d” is selected from a roughness profile of the developer-carrying member to determine the surface condition on the developer-carrying member.
As shown in FIG. 1, one mountain area and an adjacent one valley area consist of one Sm, wherein the mountain area is an area which is defined by an roughness profile line coming to an upper side of an average profile line, and the valley area is an area which is defined by a roughness profile line coming to a lower side of an average profile line.
As shown in FIG. 1, a plurality of intervals Sm (e.g., Sm1 and Sm2) are measured in the measurement-range length “d.” By averaging the values of the plurality of intervals Sm, a value of the average interval Sm can be determined.
In one example, a developer-carrying member has an average interval Sm of from 30 μm to 80 μm as above-mentioned, wherein such developer-carrying member may have a relatively larger average interval Sm compared to another conventional developer-carrying member. Thereby the above-mentioned developer-carrying member having the average interval Sm of from 30 μm to 80 μm may have a relatively mild roughness compared to another conventional developer-carrying member.
Unlike another conventional developer-carrying member carrying carriers on its surface by carrying carriers with sharp convex portions, such developer-carrying member having a relatively mild roughness on its surface can carry carriers on the developing sleeve by carrying carriers in concave portions formed on the surface of the developer-carrying member.
Therefore, such developer-carrying member having a relatively mild roughness on its surface may not change its surface shape significantly over time compared to a conventional developer-carrying member having sharp convex portions, whereby developer transportability on such developer-carrying member may be maintained over time.
Furthermore, such developer-carrying member having a relatively mild roughness on its surface rarely has sharp convex portions, whereby toner particles and external additives on carriers may not be scraped by the convex portions. If the toner particles and external additives on carriers are not scraped, toner particles and external additives will not drop into tiny concave portions on the surface of the developer-carrying member, and will not be fixed in the tiny concave portions.
However, using the average interval Sm to determine a roughness of the surface of the developer-carrying member (e.g., developing sleeve) may have a drawback as described below.
For example, assuming that a developer-carrying member has waviness on a surface of the developer-carrying member as shown in FIG. 1, such waviness is shown as a dotted line in FIG. 1.
In such a case, the average interval Sm determined based on such waviness may be construed as concave-and-convex portions formed on the surface of the developer-carrying member.
However, such waviness may not express an actual roughness profile line (shown as a solid line in FIG. 1) consisting of discrete concave and convex portions formed on the surface of the developer-carrying member, whereby an actual surface condition having discrete concave and convex portions may not be determined by the average interval Sm.
Specifically, even if actual discrete concave and convex portions exist on the surface of the developer-carrying member, the average interval Sm may show a larger value, which does not express actual concave and convex portions on the surface of the developer-carrying member, for example.
Therefore, the average interval Sm may not be a preferable indicator to determine the condition of a surface having a number of discrete concave and convex portions.
If tiny concave portions exist on the surface of the developer-carrying member, particles such as toner may adhere on such tiny concave portions. In such a case, the developer-carrying member may degrade its functions (e.g., degradation of developer transportability and developing capability) over the time.